Acylation of cyclic ketones

Acylation of steroidal saturated ketones and their enol acetates with acetic anhydride and BF₃-etherate has been studied. α-Acylketones were obtained from 3-keto, 7-keto and 16-keto steroids (I, XII and IX) in the A/B trans series and from 3-ketone (VI) in the A/B cis series. The intermediate difluoroboron chelates (II and VII) were isolated and characterized. No C-acylation of tertiary carbon atom in steroids was observed. The acylation of 2-methylcyclohexanone (XVI) and its enol acetates (XVII and XVIII) is described, and the relation between O-acylation and C-acylation is discussed. Acylation of α,β-unsaturated ketones, testosterone (XXII) and 4-methyltestosterone (XXX) for a comparative short time results in C-6 derivatives (XXIII, XXV and XXXI, and over a longer period of time in difluoroboron chelates (XXVI and XXXIII). The tautomeric equilibrium of the enolic β-diketones IV, XXVII, XXVIII, XXIX and XXXIV is also described.